Nipah virus (NiV) and Hendra virus (HeV) are related highly pathogenic zoonotic henipaviruses in the paramyxovirus family that use bats from the Pteropus genus as reservoir hosts. NiV exhibits an unusually broad host range for a paramyxovirus and infects pigs, dogs, and cats. Although first identified in an outbreak in Malaysia, near annual outbreaks in Bangladesh and India are now known to occur with average case fatality rates of 73%. HeV infections have occurred in Australia where infected horses transmitted the virus to seven humans of whom four died. Both NiV and HeV have also caused late-onset lethal encephalitis in humans. Because of their high lethality in humans, the absence of approved vaccines or treatments, and evidence of NiV human to human transmission, these viruses are NIAID Emerging Infectious Diseases/Pathogens Category C Priority Pathogens. In addition, henipaviruses can infect livestock and are serious threats to agriculture. Despite the potential for severe public health and economic consequences, research into these viruses has lagged, reflecting in part the need for biosafety level 4 containment to study replicating virus. Importantly, there are no drugs currently available to treat or prevent these infections. Recent studies have started to provide insight into the determinants of viral pathogenesis and to define at the atomic and molecular levels how transcription and replication activities are carried out by the viral RNA-dependent RNA polymerase complex (also known as the viral RDRP complex). The viral RDRP complex has obvious potential as a therapeutic target, but sensitive reliable screens and secondary assays are needed to identify and validate inhibitors of this complex. Our recent collaborative studies defined an analogous interaction between Ebola VP35 and NP proteins that is currently being developed as a therapeutic target. In order to address a major unmed need for NiV and HeV therapeutics, we will use this successful framework to develop in vitro and cell-based assays that target the interface between NiV and HeV N and P proteins. We expect to identify replication inhibitor leads targeting zoonotic henipaviruses that will facilitate biological probe and antiviral development.